Hot tap apparatus and method

ABSTRACT

A thermowell or the like is installed in a pipe or similar member without taking the member out of service by first welding an adapter to the surface of the member at the point where the thermowell is to be installed, connecting a gate valve and hot tapping machine to the adapter, drilling a hole in the member through the open gate valve, withdrawing the drill and closing the valve, replacing the drill in the hot tapping machine with the thermowell, opening the gate valve, and installing the thermowell through the open valve. The adapter having a taper internally threaded portion, distal from the ends of a conduit therethrough.

This is a division of application Ser. No. 064,772 filed Aug. 8, 1979.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to equipment for installing thermowells andsimilar devices in pipelines and other members and it particularlyrelates to a method and apparatus for the installation of thermowells,corrosion probes, injection nozzles, sampling taps and the like inpipelines and similar members without taking such members out ofservice.

2. Background of the Invention

Hot tapping machines are frequently used to permit the cutting of holesin pipes and similar members containing fluids under pressure. Such amachine normally consists of an elongated chamber containing an internalshaft to which a drill can be connected for rotary and longitudinalmovement through a packing gland at the upper end of the chamber. Thelower end of the chamber is threaded or fitted with a flange so that itcan be connected to a fitting which is welded to the surface of a pipeor other member or in some cases clamped around it. This fitting willinclude a check or gate-type valve which can be opened at the beginningof the hot tapping operation and closed at the conclusion of theoperation. This fitting is left in place after the opening in the pipeor other member has been cut. The fitting is quite expensive, generallyover $1000 and the necessity to leave it placed has made hot tapping acostly operation.

The installation of a thermowell, test probe or similar device in apipeline or other member during service normally requires hot tapping ofthe member as described above and insertion of the thermowell or otherdevice through an elongated packing gland containing a series of packingrings by means of jacking screws. This procedure is time consuming andhazardous in that the packing rings may leak and permit the escape ofhigh pressure fluids during the operation. If the pipe or other membercontains flammable gases, a fire or explosion may result. Moreover, theforce required to overcome the friction of the packing glands andinternal pressure in the system may result in bending or damage to thethermowell or other device, preventing completion of the operation andnecessitating shutdown of the system. Furthermore, if the hot tap is nolonger needed the entire fitting had to be left in place. As a result ofthese and related difficulties, conventional methods and equipment forthe installation of thermowells and similar devices in pipelines andother vessels containing fluids under pressure leave much to be desired.

SUMMARY OF THE INVENTION

The present invention provides an improved method and apparatus for theinstallation of thermowells, corrosion probes, injection nozzles, sampletaps and similar devices in pipelines and other members containingfluids under pressure which largely eliminates the difficultiesencountered with methods and apparatus employed in the past. The methodof the invention involves the welding of a novel adapter containing athreaded connection and internal seat for the thermowell or other deviceto the surface of the pipe or other member at the point where the deviceis to be installed, the connection of a gate or other full opening valveto the upper end of the adapter, and the attachment of a hot tappingmachine to the upper end of the valve. The hot tap machine comprises anelongated chamber of sufficient length to contain the drill bit andpreferably the thermowell or other device to be installed in the line.Otherwise, such a chamber must be attached to the gate valve before theinstallation of the device. Once this has been done, the valve is openedand the hot tapping machine is used to drill a hole in the wall of thepipe or other member below the adapter. The hot tapping machine drill isthen withdrawn to a point above the valve and the valve is closed toprevent the escape of fluid from the member. After this has beenaccomplished, the hot tapping machine is removed and the drill isreplaced with a special socket drive and the thermowell or other deviceto be installed. In addition to drilling, grinding may be used to makethe holes in the structure and the term "drill" as used herein, includesgrinding. The grinding is advantageous where there may be sensitiveequipment down stream from the hole, since grinding produces smallerparticles than drilling with a bit. The smaller ground particles areeasily carried away with any flow whereas the drilled particles canlodge in or catch on other equipment in the structure. This device willinclude an external threaded section for seating in the adapter and aninternal threaded section for the installation of a plug if desired orin the case of the thermowell, a temperature sensing device may beinstalled. The thermocouple or other device is placed in elongatedchamber and the special socket drive engaged in a corresponding socketin the thermocouple or other device. The valve is then opened and thehot tapping machine is used to lower the thermowell or other devicethrough the valve and threaded into place in the adapter. Thereafter,the hot tapping machine can be withdrawn from the thermowell and thevalve, chamber and hot tapping machine can be removed. The resultingthermowell occupies a minimum of space, does not require that a valve beleft in place, and can be readily removed from the pipe or other memberif this should become necessary. Simple modifications to the thermowellpermit its use as a test well, an injection nozzle, a corrosion plug, aflow indicating device, or as a housing for a flow switch, densitometer,pig indicator, annubar, or the like.

The configuration and dimensions of the adapter employed for purposes ofthe invention will depend in part upon the size and shape of the pipe orother member to which it is to be attached. Normally, however, theadapter will have generally cylindrical cross sections shaped at thebottom to fit snugly against the surface of the pipe or other memberpreferably with an internal chamber abutting the pipe terminating in afrusto-conical section and beveled externally at the lower outer edge tofacilitate its being welded in place. It will include an internalpassageway or conduit connect from the frusto-conical section andcontaining a lower seat against which a lower shoulder on the thermowellor similar device abuts, an intermediate threaded section, an upper seatagainst which an upper shoulder on the device rests, and an enlargedupper section into which the upper part of the device fits. The upperend of the adapter will be threaded on its outer surface or providedwith a flange or other means to permit attachment of the hot tappingmachine and chamber during installation of the device and the connectionin place of a cap or other closure following installation. Preferablythe internally threaded portion of the adapter is not adjacent to thelower end thereof and the lower end although generally cylindrical iscross section is thickened. By spacing the internal thread away from thelower end and thickening the body of the adapter, a heat sink isprovided, which will reduce or prevent distortion of the internalthreads when the adapter is welded to the pipe.

The thermowell or similar device employed in conjunction with theadapter will normally be an elongated tapered member having upper andlower shoulders and an externally threaded intermediate section forseating in the adapter. It will include an opening in the upper end foraccepting a rectangular or hexagonal drive member attached to the shaftof the hot tapping machine and below this may be hollow if it is to beused as a thermowell, test well or the like or solid if it is to beemployed as a corrosion probe. Below the drive opening, an internallythreaded section will normally be provided in devices intended for useother than a corrosion probe to permit the insertion of a threaded plug.The lower portion of the device may have a variety of differentconfigurations, depending upon the particular use for which the deviceis intended.

The type of chamber, valve and other parts used in installing thethermowell or similar device will depend to a large extent upon theparticular type of hot tapping machine employed. These may be providedwith either threaded or flanged connections and may be varied in size,depending upon the size of the pipe or the like with which the apparatusis to be employed, the length of the thermowell or similar device to beinstalled, and the dimensions of the particular hot tapping machine tobe used.

The method and apparatus of the invention have numerous advantages overconventional systems used in the past. The system of the inventionpermits the installation, while a pipeline or similar vessel is inservice, of thermowells and other devices similar to those installedduring the original construction, eliminates the need for jacking screwsor other devices normally required to insert thermowells through packingrings or gland seals and does away with the necessity for such rings orseals. Because the thermowell does not need to extend through anisolation valve and packing when in place, it can be considerablyshorter than the devices generally employed. The method and apparatusare considerably less expensive than systems currently in use since onlythe adapter and the thermowell or other device are left in place, andpermit thermowell installation more rapidly than do conventionalsystems. There is little danger of fluid leakage or damage to thethermowell during installation and little chance of malfunctioning ofthe apparatus of the invention. Should a malfunction occur duringinstallation, the work can be rapidly terminated with little danger andwithout necessity for shutting down the pipeline or other vessel. Theinstallation equipment employed can be reused and need not be left inplace. Thermowells and other devices installed in accordance with theinvention can be readily removed or replaced as necessary. As a resultof these and other advantages, the system of the invention haswidespread potential application.

A related aspect of the present invention, is the thread chaser orcleaning device which is used to remove particles, which result fromdrilling or grinding, from the internal threads of the adapter.

The thread chaser comprises a body having means to attach to a driveshaft, a conical section having pipe threads thereover, a pair ofintersecting slots extending through said conical section and dividingit into quadrants and preferably a bore extending along the axis of theintersection of said slots and exceeding the diameter of saidintersection. Preferably, the slots are substantially the same size andlength and intersect at right angles, with the slots extending at leastthe length of the conical section. That is, the slots preferably extendlaterally and vertically through the conical section, cutting the coneinto four equal sections extending from the upper part of the chaserbody.

The slots and bore allow the threaded conical section to bend and followthe internal threads of the adapter. The threads on the chaser willcorrespond to the threads to be cleaned in the adapter. The threadchaser may be made of steel or plastic, and preferably it is magnetizedto help capture some of the cuttings from the drilling or grindingoperation. A plastic composition containing powdered iron as known inthe art serves this function and is unlikely to damage the threads inthe adapter.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a vertical view, partially in section illustrating theinstallation of a thermowell in a pipeline in accordance with theinvention.

FIG. 2 depicts a finished thermowell installed in an adapter inaccordance with the invention in cross sectional elevation.

FIG. 3 shows an adapter according to the present invention in crosssectional elevation.

FIG. 4 shows an elevation of a thread chaser.

FIG. 5 shows a cross sectional view of the thread chaser along lines5--5 of FIG. 4.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS

FIG. 1 illustrates the apparatus used for boring the hole and forsetting the device (a thermowell 16a in this case) in the adapter 18.

The adapter 18 is welded 21 to pipe 19. The gate valve 17 is attached tothe adapter and chamber 13 composed of two joined sections is attachedon top of the valve. The upper end of the chamber is closed and shaft 11extends through seal 14 into the chamber. The shaft 11 is connected tohandle 10 by sprocket 22. The shaft is movable both rectilinearly androtationally.

Attached to shaft 11 by pin 12 is sprocket device 15 which engages in acorresponding socket in thermowell 16, which is depicted in phantomoutline showing it before being seated in the adapter 18. Thermowell 16ais shown seated in adapter 18 extending through hole 20 into pipe 19.

To explain how the thermowell came to be seated in the adapter,reference is again had to FIG. 1. In sequence, the steps of the processare:

1. Weld adapter 18 to pipe 19 (welds 21).

2. Attach gate valve 17 and chamber 17a in that order to the adapter 18.

3. Attach a drill bit (not shown) to shaft 11 in place of sprocketdevice 15. If the chamber 13 is composed of two sections as shown inFIG. 1, it is convenient to separate the section at 23 for changing theattachments to shaft 11 and inserting the device for installation in theadapter 18.

4. Passing the shaft and attach drill bit through open gate valve 17,through the adapter and onto the surface of pipe 19.

5. Rotating shaft to cause the drill bit to cut hole 20 in pipe 19. Thebit could be rotated by hand, however, ordinarily a power source such asan air motor or electric motor would be connected to sprocket 22. Thedrill is sized to be slightly smaller than the smallest portion of theconduit (i.e., section 45) thereby providing a drill guide.

6. After the hole 20 is completed, the shaft and drill bit are raisedabove gate valve 17 and the valve is closed.

7. The chamber 13 is opened, e.g., at 23 and the drill bit removed andreplaced with sprocket device 15 and the thermowell or other device 16attached thereto and the chamber 13 closed. After the hole is drilled,it is preferable to clear the internal threads in adapter 18 with threadchasing or cleaning device.

8. The gate valve 17 is opened and the shaft, sprocket device andthermowell lowered to pass the thermowell through the adapter 18 intothe pipe. The taper of the middle portion of the internal passagethrough the adapter as well as the chamber (bevelled surface 37 FIG. 2)aid in guiding the device 16a into the correct position.

9. Then using the handle 10 the device 16a is screwed into the adapterforming a metal to metal seal by means of the taper of the threadedconnecting portions.

10. The sprocket device is withdrawn and the hot tap portion and thevalve removed from the adapter.

During those times in which the chamber 13 is subject to contact withthe contents of the pipe 19, it is best to maintain a pressure in thechamber equal to or greater than that in the line. An inlet 24 isprovided for this purpose. The gas is preferably an inert, such asnitrogen. The pressuring of the system will also show if the system hasbeen properly prepared, hence avoiding an unexpected leak after the pipeis drilled.

The heart of the invention, i.e., that which makes the simplifiedprocess and reduced cost possible is the adapter. It can be readilyappreciated as mentioned above that any number of useful devices can beinexpensively set in the adapter, once it is attached to the pipe orother member.

FIG. 2 illustrates the adapter 30 in detail with a thermowell device 31situated therein and FIG. 3 depicts the adapter 30 alone. The adaptercomprises a body 48 having circular cross section and generallycylindrical shape although the diameter of the cross section may vary,and having an internal conduit extending therethrough along the centralaxis thereof. One end is adapted to be welded onto a pipe and has anexternally bevelled surface 41 thereabout the opening. Extendinginwardly from the bevelled end is an enlarged portion 40 of the internalconduit 44, which portion has a frusto-conical shape 42 on the interiorsection thereof. Frusto-conical section 42 (a bevelled surface)connector to a narrowed portion 45 of the conduit 44 which connects toan enlarged tapered section 46 having a bevelled surface 37, adjoiningthe narrowed portion 45, and having internal tapered thread 36. Thebevelled surface 37 forms a first shoulder in section 46.

The body 48 preferably has a greater cross section in the area of thefrusto-conical section 42 and the narrowed section 45. The enlargedchamber 44 is tapered down in diameter toward the bevelled surface 37.The tapered threaded surface when engaged with a device 31 by threads 35thereon causes a metal to metal seal seating the device on the bevelledsurface 37. Connecting to the enlarged end of tapered section 46 is theupper chamber 47 which is of larger cross section than tapered sectionchamber 46. There is a bevelled surface 38 in upper chamber 47 adjoiningtapered section 46. Surface 38 insures self aligning with the externalthreads of thermowell which is also chamfered. The bevelled surface 38forms a second shoulder in section 47. External of the adapter aboutupper chamber 47 means 43 are provided to attach a valve, which arethreads in this embodiment, however a flange would work as well. Thetaper of chamber 46 and the chamfer of bevelled surface 37 aid inpositioning a device in the adapter.

The device 31 seated in adapter 30 may have a chamber 34 therein as in athermowell with a socket 33 adapted to receive the sprocket device 15and an internally threaded section 32 for inserting a cap or temperaturemeasuring devices. A spring loaded ball plunger (not shown) on thesprocket device 15, engages in annular groove 49 in socket 33 or insimilar grooves in other items fitted to the adapter 30, which preventsthe item from falling off of the sprocket device 15, but allowswithdrawal of the sprocket device once the item, for example, thethermowell 31, is threaded into adapter 30.

The frusto-conical section 42 provides an important function during thedrilling of the hole in the pipe in that the cuttings made by the drillbit are wiped off and collected in chamber 40 and hence are not broughtback up to the upper portion of the adapter 30 or into the valve orupper portion of the apparatus where they would be a problem in removal.In any event, it is the better practice after the hole is drilled in thepipe to attach a thread cleaning or chasing device to the shaft and toclean out the threads since even small drilled particles can cause animperfect sealing between threads 36 and 37.

In an embodiment not shown and less preferred, the narrowed portion 45of the internal conduit 44 may be omitted thereby bringing taperedsection 46 and frusto-conical section 42 together. This embodiment isfully operable, however, the internal threads 36 are brought into closerproximity to bevelled surface 41 where the weld is to be made, whichincreases the likelihood of distortion of the threads from the welding.

The term "central axis" is used to mean the axis through the circularcross-sections of the adapter.

The thread chaser shown in FIG. 4, comprises a body 50 which has acylindrical portion 50a and conical section 51. The taper of the conicalsection corresponds to the taper of the threads in the adapter to becleaned. There is chamfer 55 about the distal end of the conical sectionwhich aids in aligning the chaser in the adapter. A pair of slots 52extend through the conical section intersecting at right angles as shownin FIG. 5 creating four substantially equal quadrants. In addition toslots, a bore 53 extends along the axis of the slots intersection andslightly beyond into the body of the chaser. The slots and bore make theconical section bendable to accommodate to the threads in the adapter.The slots extend somewhat into cylindrical section 50a to allowflexibility in the entire conical section.

Over the surface of the conical sections 51 are machine threads 54 whichare the same as those in the adapter and of course any thread desiredmay be employed.

At the end of the body 50 distal to the conical section, a socket 56(phantom lines) is provided with an annular groover 57, to engage thesprocket device 15 as described above.

The invention claimed is:
 1. A method for making a hot tap to a pipe orother member being in use and carrying high pressure materialstherethrough comprising:(1) welding an adapter comprising a body havinga generally cylindrical shape and a conduit therethrough along thecentral axis of said body, said body having internal threads located ina tapered section of said conduit, intermediate the ends of said bodyand distal therefrom for forming a metal to metal bond with a deviceseated therein and having means for attachment to a valve at one end ofsaid body and being bevelled externally at the other end for welding topipe or other member, (2) attaching a valve and elongated hollow memberthereto forming a substantially cylindrical closed chamber having a sealat the top thereof and having a shaft located therethrough, said shaftbeing rectilinearnally and rotationally movable in said chamber, (3)attaching a drill bit to said shaft, (4) drilling a hole in said pipewhile the valve is open, (5) withdrawing the shaft and drill bit abovesaid valve, (6) closing said valve, (7) replacing said drill bit with adevice having of a size and configuration to seat in said adapter havingthreads on the surface thereof adapted to form a metal to metal bondwith the threads in said adapter in said tapered section, (8) openingthe valve, (9) lowering the shaft and device to place said device insaid adapter and rotating said shaft to seat said device in said adapterwherein when said device, having an elongated configuration, an upperportion, an intermediate portion having threads thereon and a lowerportion, is seated in said adapter, the intermediate portion is engagedwith the threads of the tapered section, said upper portion generallyextends beyond said adapter toward said valve and the lower portiongenerally extends beyond said adapter toward said hole in said pipe,(10) withdrawing shaft to disconnect it from said device.
 2. The methodaccording to claim 1 wherein after the shaft is withdrawn to disconnectit from said device, the valve and chamber are removed leaving only theadapter and the device seated therein attached to the pipe or members.3. The method according to claim 1 wherein a gas pressure greater thanthe pressure in the pipe or member is applied to said chamber.
 4. Themethod according to claim 1 wherein the drill bit is sized to slightlysmaller than the narrowest portion of the conduit through said adapter.